Which of these types of ionizing radiation is most penetrating?

Gamma rays are the most penetrating type of ionizing radiation because they possess high energy and, unlike alpha and beta particles, they do not carry an electric charge. This lack of charge allows gamma rays to travel through materials more easily without being deflected. Their high energy enables them to pass through dense substances, including metals and human tissue, to a much greater extent than alpha and beta particles.

Alpha particles, being heavy and positively charged, are mostly absorbed by a few centimeters of air or by human skin. Beta particles can penetrate further than alpha particles but are still limited in their range and can be stopped by a few millimeters of plastic or glass. Neutrons, while being highly penetrating, typically require more complex interaction mechanisms and often depend on the type of material they are interacting with to be effectively stopped.

In comparison, gamma rays consistently exhibit the highest penetrating power, making them a significant concern in radiological safety, especially in medical and nuclear environments.